1. FALL 2005 CSI 4118 – UNIVERSITY OF OTTAWA 1
Part 4
Other Topics
RPC & Middleware

2. FALL 2005 CSI 4118 – UNIVERSITY OF OTTAWA 2
Middleware
 Tools to help programmers
 Makes client-server programming
 Easier
 Faster
 Makes resulting software
 Less error-prone
 More reliable

3. FALL 2005 CSI 4118 – UNIVERSITY OF OTTAWA 3
Middleware Approach
 Allow programmer to work with familiar
language constructs
 Provide tools to help programmer
 Special translators
 Libraries
 Automatically generate code for
 Network communication
 Connection management

4. FALL 2005 CSI 4118 – UNIVERSITY OF OTTAWA 4
Remote Procedure Call
 Uses standard procedure call paradigm
 Divides program along procedure call
boundaries
 Main program and procedures for user interaction
in client side
 Other procedures in server side

5. FALL 2005 CSI 4118 – UNIVERSITY OF OTTAWA 5
Reason for Remote Procedure
Call
If a programmer follows the same procedure
call paradigm used to build conventional
programs when building client and server
software, the programmer will find the task
easier and will make fewer mistakes

6. FALL 2005 CSI 4118 – UNIVERSITY OF OTTAWA 6
Illustration of Conventional
Procedure Call Graph
 Arrow denotes procedure call

7. FALL 2005 CSI 4118 – UNIVERSITY OF OTTAWA 7
Procedure Call Graph Divided
Into Client and Server
 Division occurs on call boundary
 Main program in client piece

8. FALL 2005 CSI 4118 – UNIVERSITY OF OTTAWA 8
Communication Stubs
 Inserted to enable remote “call”
 Automatically generated
 Use original call interface
 Allow calling and called procedure to remain
unchanged

9. FALL 2005 CSI 4118 – UNIVERSITY OF OTTAWA 9
Illustration of Client and Server Stubs
 Original call in (a)
 Same interface with stubs in (b)

10. FALL 2005 CSI 4118 – UNIVERSITY OF OTTAWA 10
Creating Stubs
 Programmer writes
 Code for a program
 Specification of procedure interfaces using
Interface Definition Language (IDL)
 Middleware generates
 Client and server stub code
 Necessary socket calls
 Data translation

11. FALL 2005 CSI 4118 – UNIVERSITY OF OTTAWA 11
Data Representation
 Network can connect heterogeneous
computers
 Two computers may use different
 Integer representations
 Character codes
 Floating point representations
 Translation required

12. FALL 2005 CSI 4118 – UNIVERSITY OF OTTAWA 12
Possible Data
Translation Schemes
 Use receiver’s representation
 Sender translates all outgoing data
 Use sender’s representation
 Receiver translates all incoming data
 Use external representation (popular)
 Sender translates to external form before sending
 Receiver translates from external form after
reception

13. FALL 2005 CSI 4118 – UNIVERSITY OF OTTAWA 13
Middleware Technologies That
Use Remote Procedure Call
 ONC RPC
 Open Network Computing
 IETF standard
 Popular in Unix world
 DCE RPC
 Distributed Computing Environment
 Open Group Standard

14. FALL 2005 CSI 4118 – UNIVERSITY OF OTTAWA 14
Middleware Technologies That
Use Remote Procedure Call
(continued)
 MSRPC
 Microsoft
 Variant of DCE RPC

15. FALL 2005 CSI 4118 – UNIVERSITY OF OTTAWA 15
Object-Oriented Middleware
 Designed for use with object-oriented
programming languages
 Same general scheme as RPC
 Interface Definition Language
 Tool to build stubs
 Libraries to handle network communication
 Uses method invocation instead of procedure
call

16. FALL 2005 CSI 4118 – UNIVERSITY OF OTTAWA 16
Middleware Technologies That
Use Remote Object Invocation
 CORBA
 Common Object Request Broker Architecture
 Well known object-oriented middleware
 MSRPC2
 Microsoft
 Also called Object RPC (ORPC)

17. FALL 2005 CSI 4118 – UNIVERSITY OF OTTAWA 17
Middleware Technologies That
Use Remote Object Invocation
 COM / DCOM
 Also from Microsoft
 Component Object Model (COM)
 Used on single computer
 Provides mechanism for inter-object references
 Distributed Component Object Model
 Used across multiple computers
 Includes communication stubs

18. FALL 2005 CSI 4118 – UNIVERSITY OF OTTAWA 18
Middleware Technologies That
Use Remote Object Invocation
 RMI
 From Sun Microsystems
 Methods of remote Java objects can be invoked
from other Java virtual machines on different
hosts
 Jini
 Also from Sun; based on Java
 Provides an environment for creating
dynamically networked components,
applications, and services that scale

19. FALL 2005 CSI 4118 – UNIVERSITY OF OTTAWA 19
Summary (continued)
 Middleware
 Tools to help build client and server
 Automates routine tasks
 Two popular paradigms
 Remote procedure call
 Object invocation
 Generates communication stubs